Just noticed this after getting my supersprint exhaust installed with race pipes..... under normal acceleration the car sounds normal but noticed if i'm giving the car decent amount of throttle sometimes i hear a strange fart sound right after it UPSHIFTS. Happens for only a split second and seems to only happen when the car is under a certain load...

Strange sound for a backfire. My manual 335 backfired only if I was going WOT and shifted near redline. Sounded more like a loud pop or mini explosion where as the F10 sounds like deep sounding fart lol. I was looking it up and seems like all the Audi/VW with the DSG transmission has a similar sound during a upshift too.

Sounds as if the exhaust goes from positive pressure to negative pressure (vacuum) for a split second during the upshift.